The area of polymer blends has been the subject of increasing interest because of the ability to tailor the properties of the resulting blend based on the properties of the starting polymers. Cellulose acetate polymers are generally not compatible (yield clear films with a single glass transition temperature) with other polymers. One area of particular interest is in the preparation of solid, homogenous water insoluble polymer/water soluble polymer miscible blends for controlled release applications. The combination of a water insoluble polymer and a water soluble polymer in a miscible blend imparts unique swelling properties to the blend. The extent of swelling is controlled by the type and amount of the water soluble components (polymer and additives) and not exclusively by the pH of the solution.
Prior work on mixtures of cellulose acetate and polyvinylpyrrolidinone (PVP) includes U.S. Pat. No. 4,743,248 which discloses osmotic pump type tablets comprised of sequential layers of a pH sensitive water soluble polymer (such as PVP) and insoluble polymers (such as cellulose acetate). The device disclosed employs a very small hole which is used to release the active ingredient.
U.S. Pat. No. 4,771,089 described polymer blends which absorb at least their own weight of water. The films shown in the examples were cast from N,N-dimethylacetamide which is not a very desirable solvent because of its high boiling point and the difficulty of removing all of the solvent from the film.
EP 317, 274 discloses the use of blends of cellulose esters with PVP to coat medicaments in a fluidized bed for chewable tablets. The coating serves to mask the taste of the medicament and still deliver the medicament.
U.S. Pat. No. 5,120,548 discloses a controlled release drug delivery device comprising controlled release swelling modulators with swellable polymers using holes or pores for release.
EP-A-0335560 filed on Mar. 21, 1989 discloses a controlled release pharmaceutical preparation, comprising a core containing a pharmaceutically active ingredient, and a porous film of a hydrophobic polymeric substrate or a hydrophobic polymeric substance and a hydrophilic polymeric substance, the core being coated with the porous film.
EP-A-0473431 filed on Aug. 29, 1992 discloses a composition coated with a blend of cellulose acetate and PVP.
However, none of the references disclose a uniformly dispersed controlled release matrix system comprising a blend of cellulose acetate and PVP and an active ingredient.